HELGOL.~NDER MEERESUNTERSUCHUNGEN Helgol~nder Meeresunters. 49, 393-398 (1995)
Tube-building in two epifaunal amphipod species,
C o r o p b i u m i n s i d i o s u m
and
Jassa falcata
I. Ulrich 1, K. A n g e r 1 & U.
S c h S t t l e r 2I Biologische A n s t a l t Helgoland (Meeresstation); D-27498 Helgoland, G e r m a n y 2 F o r s c h u n g s z e n t r u m Jfihch, A uflenstelle Warnemfinde; D-18119 Rostock- Warnem~inde,
G e r m a n y
ABSTRACT: Jassa falcata and Corophium insidiosum are epifaunal tube-building marine amphipods, whose niches overlap in habitat and food requirements. Laboratory experiments were conducted to study the influence of the quality of different available particulate substrates on settlement and tube-building behaviour of these two amphipod species. Our experiments suggest that C. insidiosum is less specialized in this respect than J. falcata. C. insidiosum is able to use organic materials for tube-building such as artificial ( Ulva spec. powder) or mixed natural detritus as well as inorganic material (coarse sand); whereas J. falcata utilizes organic materials, but sand only to a very limited extent
I N T R O D U C T I O N
In g e n e r a l , r o c k y s h o r e s s h o w a m u c h h i g h e r s p e c i e s d i v e r s i t y w h e n c o m p a r e d to soft b o t t o m c o m m u n i t i e s a n d h e n c e s h o u l d r e q u i r e a h i g h e r d e g r e e of e c o l o g i c a l s p e c i a l i z a - tion in t h e i r f a u n a . O n e of t h e s p e c i f i c d i f f i c u l t i e s of h a r d - b o t t o m d w e l l e r s c o n c e r n s f i x i n g t h e m s e l v e s to t h e g r o u n d , so t h a t t h e y c a n n o t b e w a s h e d a w a y b y s t r o n g w a t e r m o v e - m e n t s . T u b e - b u i l d i n g is a c o m m o n a d a p t a t i o n to this p a r t i c u l a r h a b i t a t r e q u i r e m e n t .
A m p h i p o d s b e l o n g to t h e m o s t n u m e r o u s a n d t a x o n o m i c a l l y d i v e r s e c o m p o n e n t s of e p i f a u n a l m a r i n e i n v e r t e b r a t e c o m m u n i t i e s (Jacobi, 1987). M o s t of t h e m l i v e h e m i s e s s i l e in t u b e s w h o s e w a l l s consist of b o d y s e c r e t i o n s a n d e x o g e n o u s m a t e r i a l s . T h e i r settle- m e n t b e h a v i o u r is i n f l u e n c e d by e n v i r o n m e n t a l f a c t o r s s u c h as c u r r e n t s , t h e s u b s t r a t e s u r f a c e , a n d t h e a v a i l a b i l i t y of t u b e - b u i l d i n g m a t e r i a l s . In t h e p r e s e n t i n v e s t i g a t i o n , t h e i n f l u e n c e of t h e t y p e of b u i l d i n g m a t e r i a l s o n s e t t l e m e n t a n d t u b e - b u i l d i n g b e h a v i o u r w a s c o m p a r e d in t w o v e r y c o m m o n , c o e x i s t i n g a n d p o t e n t i a l l y c o m p e t i n g a m p h i p o d s p e c i e s , Jassa falcata a n d Corophium insidiosum.
M A T E R I A L S A N D M E T H O D S
394 I. Ulrich, K. A n g e r & U. SchSttler
from the laboratory s e a w a t e r filter system a n d stored until use at 12~ S a n d w a s t a k e n from the s o u t h e r n b e a c h of H e l g o l a n d a n d fractionated by p a s s i n g it t h r o u g h sieves with 300 a n d 500 gm m e s h widths.
A m p h i p o d s were put into plastic a q u a r i a (17.7 x 11.4 cm bottom area) which r e c e i v e d s e a w a t e r from a f l o w - t h r o u g h system (ca. 0.3 1/min) a n d h a d d r a i n a g e holes 5 cm above the bottom to g u a r a n t e e a c o n s t a n t w a t e r level. With each species, experi- m e n t s with 3 substrate types (Ulva spec. powder, m i x e d n a t u r a l detritus, coarse sand; 3 replicate aquaria, with 30 i n d i v i d u a l s each) were carried out over o b s e r v a t i o n periods of 19 days. A p p r o x i m a t e l y e q u a l a m o u n t s (by volume) of the following b u i l d i n g materials were initially a d d e d to the aquaria: 0.4 g Ulva spec. powder; 10 ml n a t u r a l detritus; 10 ml coarse s a n d (300-500 gm grain size fraction).
The a q u a r i a bottoms were e x t e r n a l l y m a r k e d dividing their area into r e c t a n g l e s of 2.85 x 2.95 cm. Data sheets with identical p a t t e r n s w e r e prepared, a n d each d a y the total n u m b e r a n d location of complete t u b e s w e r e r e c o r d e d on a n e w sheet. T u b e - b u i l d i n g was c o n s i d e r e d c o m p l e t e d w h e n the a m p h i p o d s could fully retract into t h e m after b e i n g m e c h a n i c a l l y disturbed.
RESULTS
A r t i f i c i a l d e t r i t u s ( U l v a s p e c . p o w d e r )
Figure 1 shows the t u b e - b u i l d i n g activity of CoropN'um insidiosum a n d Jassa falcata
d u r i n g a 19-day observation period with exclusively Ulva spec. p o w d e r s u p p l i e d as a substrate. A m a r k e d difference in t u b e - b u i l d i n g b e h a v i o u r was observed b e t w e e n the two a m p h i p o d species. After only o n e day, on a n a v e r a g e 70 % of the C. i n s i d i o s u m had constructed tubes. D u r i n g the later course of the experiment, the a v e r a g e p e r c e n t a g e of i n d i v i d u a l s that h a d built t u b e s r a n g e d b e t w e e n 70-85, s h o w i n g no m a r k e d i n c r e a s e with time. In contrast, only 10% of .L falcata c o n s t r u c t e d tubes within the first d a y of the experiment, b u t the n u m b e r of t u b e s i n c r e a s e d c o n t i n u a l l y d u r i n g the course of the e x p e r i m e n t to a final a v e r a g e of a b o u t 60 % (Fig. 1). With Ulva spec. detritus. C. insid- iosum built significantly more t u b e s t h a n J. falcata (days 1-5: p < 0 . 0 0 0 1 ; days 8-12: p < 0.001; days 15-19: p < 0 . 0 5 ; o n e - w a y ANOVA).
M i x e d n a t u r a l d e t r i t u s
W h e n n a t u r a l detritus was g i v e n as a b u i l d i n g material, 5 1 % of the Corophium insidiosum b u i l t a t u b e d u r i n g the first d a y of observation, s h o w i n g a g r a d u a l i n c r e a s e d u r i n g the course of the e x p e r i m e n t , a n d e v e n t u a l l y r e a c h e d a m a x i m u m of 86 % (Fig. 2). In Jassa falcata, the p e r c e n t a g e of i n d i v i d u a l s that built a tube i n c r e a s e d over the first 9 days to m a x i m u m levels b e t w e e n 50-73 %. According to a o n e - w a y A N O V A , d u r i n g the first 12 days significantly more t u b e s w e r e built b y C. insidiosum t h a n b y J. falcata.
Later, however, the difference w a s no l o n g e r statistically significant (days 1-5: p <0.0001; days 8-12: p <0.05; days 15-19: p > 0.05}.
E o a r s e s a n d
T u b e - b u i l d i n g in a m p h i p o d s 395
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Time (days)
Fig. 1. T u b e - b u i l d i n g in dassa falcata a n d Corophium insidiosum g i v e n artificial detritus (Ulva spec. p o w d e r ) as a s u b s t r a t e . P e r c e n t a g e of a n i m a l s b u i l d i n g a t u b e d u r i n g the 19-day o b s e r v a t i o n p e r i o d (n = 30 individuals in e a c h replicate); error b a r s = arithmetic m e a n • 1 s t a n d a r d deviation (n = 3
replicate e x p e r i m e n t s )
b e o b s e r v e d w h e n coarse s a n d was offered as a substrate (Fig. 3). D u r i n g the first d a y of observation, 42 % of the i n d i v i d u a l s built a t u b e with this m a t e r i a l D u r i n g the course of the e x p e r i m e n t , this i n c r e a s e d to a b o u t 8 0 - 9 1 % .
Jassa
falcata, in contrast, was hardly able to use s a n d as a b u i l d i n g material. D u r i n g the 19-day observation period, n e v e r more t h a n a n a v e r a g e ot a b o u t 8 % (i.e. 2 individuals) lived in tubes. The difference b e t w e e n the two a m p h i p o d species c o m p a r e d here was statisticallv significant d u r i n g the entire course of the e x p e r i m e n t (consistently p < 0.05).DISCUSSION
396 I. Ulrich, K. A n g e r & U. S c h 6 t t l e r
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=
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0
5
10
15
2 0
Time (days)
Fig. 2. Tube-building in Jassa falcata and Corophium insidiosum given mixed natural detritus as a substrate. Percentage of animals building a tube during the 19-day observation period (n = 30 individuals in each replicate); error bars = arithmetic mean ___ 1 standard deviation (n = 3 replicate
experiments)
in t h e s a m e c a t e g o r y of t u b e - b u i l d e r s as L. pilosus ( G o o d h a r t , 1939), w h e r e a s J. falcata.
w h i c h u t i l i z e d a l m o s t e x c l u s i v e l y o r g a n i c m a t e r i a l , m a y n o t fit into a n y g r o u p w i t h i n this s c h e m e .
Corophium insidiosum a n d Jassa falcata differ n o t o n l y in t h e u s e of b u i l d i n g m a t e r i a l , b u t also in t h e t i m e n e e d e d for t u b e c o n s t r u c t i o n . C. insidiosum c a n c o n s t r u c t t u b e s e q u a l l y wel] u s i n g v e r y d i f f e r e n t m a t e r i a l s s u c h as c o a r s e s a n d . fine n a t u r a l detritus, or c o a r s e p a r t i c l e s of g r o u n d m a c r o a l g a e . H o w e v e r , t h e l a t t e r m a t e r i a l s e e m e d to b e p r e f e r r e d , a n d c o l o n i e s b u i l t w i t h this m a t e r i a l g r e w f a s t e r t h a n t h o s e u s i n g o t h e r s u b s t r a t e s . In g e n e r a l , c o l o n i z a t i o n a n d t u b e - b u i l d i n g b y C. insidiosum o c c u r r e d q u i t e r a p i d l y , a n d a f t e r o n l y a f e w d a y s m o s t of t h e a n i m a l s h a d c o n s t r u c t e d t h e i r o w n t u b e .
Jassa falcata, in contrast, w a s a l m o s t c o m p l e t e l y r e s t r i c t e d to t h e u s e of o r g a n i c m a t e r i a l , d e m o n s t r a t i n g difficulty in i n c o r p o r a t i n g s a n d b u t s h o w i n g n o p r e f e r e n c e b e t w e e n c o a r s e (Ulva spec.) or f i n e (mixed) d e t r i t u s . C o l o n i z a t i o n b y J. falcata w a s s l o w e r t h a n
C. insidiosum. A f t e r 10 d a y s of o b s e r v a t i o n , o n l y < 5 0 % of t h e a n i m a l s h a d built a t u b e , r e g a r d l e s s of t h e t y p e of a v a i l a b l e m a t e r i a l . In s u m m a r y , C. m s i d i o s u m a p p e a r s to b e in t h i s r e s p e c t a m u c h m o r e f l e x i b l e (or o p p o r t u n i s t i c ) c o l o n i z e r as o p p o s e d to Jassa falcata.
A p o s s i b l e c a u s e for d i f f e r e n t c a p a b i l i t i e s t o u s e s a n d a s a b u i l d i n g m a t e r i a l m i g h t b e a c o n s i s t e n c e d i f f e r e n t i a l of t h e s p e c i f i c s e c r e t i o n p r o d u c t s u s e d for t u b e c o n s t r u c t i o n .
T u b e - b u i l d i n g in a m p h i p o d s 397
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9 -
80
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40
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~
o
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z z
0
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Time (days)
Fig. 3. Tube-building in Jassa falcata and Corophium insidiosum given coarse sand (300-500 ~m grain size) as a substrate. Percentage of animals building a tube during the 19-day observation period (n = 30 individuals in each replicate); error bars = arithmetic mean _+ 1 standard deviation
(n = 3 replicate experiments)
a q u a r i a w a i l s u s i n g t w e e z e r s . In J. falcata, s u c h s o l e l y s e c r e t e d , p a r t i c l e - f r e e t u b e s w e r e u n s t a b l e a n d w e r e a l w a y s d e s t r o y e d w h e n r e m o v e d . T h i s s u g g e s t s t h a t t h e s e c r e t i o n p r o d u c t s of t h e l a t t e r s p e c i e s m a y n o t b e c o h e s i v e e n o u g h to p e r m a n e n t l y g l u e c o a r s e s a n d p a r t i c l e s .
T h e d i f f e r e n t u s e by Corophium insidiosum a n d Jassa falcata of a v a i l a b l e b u i l d i n g m a t e r i a l p r o v i d e s a n e c o l o g i c a l a d v a n t a g e for t h e f o r m e r in d e v e l o p i n g n e w c o l o n i e s on b a r e h a r d b o t t o m s w i t h little s e d i m e n t a t i o n . H o w e v e r , b o t h s p e c i e s a r e f r e q u e n t l y f o u n d t o g e t h e r in t h e s a m e h a b i t a t a n d o f t e n in c l o s e v i c i n i t y to e a c h o t h e r (Karez, 1991; A n g e r , 1979). T h i s m i g h t b e e x p l a i n e d b y a f a c i l i t a t i o n e f f e c t d u r i n g e a r l y c o l o n i z a t i o n : t h e o p p o r t u n i s t i c s e t t l e r C. insidiosum c a n o c c u p y f r e e s p a c e w h i c h is u n s u i t a b l e for J. falcata
a n d , as a s u s p e n s i o n f e e d e r , m a y a c c u m u l a t e fine p a r t i c l e s a r o u n d its t u b e s . T h i s m a y s l o w l y c h a n g e t h e c h a r a c t e r of t h e s u r r o u n d i n g m i c r o h a b i t a t (Mills, 1969), f a c i l i t a t i n g l a t e r s e t t l e m e n t a n d t u b e - b u i l d i n g b y J. falcata, O n t h e o t h e r h a n d , t h e m o r e o p p o r t u n i s - tic s p e c i e s , C. insidiosum, s h o u l d b e a b l e to e a s i l y c o l o n i z e h a b i t a t s t h a t a r e a l r e a d y o c c u p i e d b y J. falcata p o p u l a t i o n s . M u t u a l c o m p e t i t i o n for t u b e - b u i l d i n g m a t e r i a l is r e s t r i c t e d in t h e s e t w o s p e c i e s , as C, insidiosum c a n u s e a n y m a t e r i a l , i n c l u d i n g t h a t w h i c h is d i s c a r d e d b y J. falcata,
3 9 8 I. U l r i c h , K. A n g e r & U . S c h 6 1 t l e r
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